System comprising sound reproduction means and ear microphones

ABSTRACT

A sound recording and reproduction system comprises ear microphones for recording sound and sound reproduction means for generating sound and means to control the sound signal generated by said sound reproduction means. The system comprises storing device ( 2 ) for storing sound signals recorded by the microphones (M_R,M_L), and an input ( 24 ) for reproduction of a recorded sound signal (S 3 ) on the means for generating sound (LS_R,LS_L) through an adaptive filter ( 21 ). The system comprising a feed back system ( 25 ) comprising the input ( 24 ), the adaptive filter ( 21 ), at least an ear microphone (M_R,M_L), at least one sound reproduction means (LS_R,LS_L) and a comparison means ( 22 ) for comparing an input signal (S 3 ) to a signal received by the microphone (S 6 ) upon during reproduction of said input signal (S 3 ), said comparison means ( 22 ) providing a comparison signal (e) for regulating the adaptive filter ( 21 ).

The invention relates to a sound recording and reproduction systemcomprising ear microphones for recording sound and sound reproductionmeans for generating sound and means to control the sound signalgenerated by said sound reproduction means.

Sound reproduction means are used in and for audio equipment such as(mobile) CD-players and comprise e.g. headphones.

Ear microphones are within the concept of the invention to beinterpreted as microphones for use in or close to the ear or ears of aperson.

The sound reproduction means, e.g. headphones, comprise a means forgenerating sound (usually a small loudspeaker). A recorded sound signal(voice or music) is sent to the headphone(s) and sound generators insidethe headphone generate a sound. The listener will, however, perceive thegenerated sound as being generated inside or very near the head or morein general at the position of the sound reproduction means (where infact it is generated) unless the sound signal is adapted. An unadaptedsound is perceived to be unnatural. It is known to overcome suchobjections at least partially by recording the sound by means of amicrophone in the ears using so called binaural recording. Althoughbinaural recording improves the perception of sound, problems remain. Animportant aspect in this respect is the transfer characteristics ofsound by an external source to the head and pinnae itself, the so-calledHead Related Transfer Function (HRTF), i.e. the manner in which soundbecomes attenuated and altered by the head and pinnea itself before itactually is heard.

Using binaural recordings a ‘standard head’ is usually used. The HRTF'sare dependent on the actual shape and form of the head and the ear anddiffer substantially from one person to another. Furthermore, dependingon the position of the microphones, the recorded sound, while beingplayed back through the headphones, has travelled twice through the earcanal or has been influenced twice by the pinnae, which makes the soundreproduction sound not the same as during the recording. Furthermore thetransfer function of the headphone itself has a detrimental influence onsound production. Although there has been made use of equalizers tolessen these detrimental effects such equalizing means only partiallyovercome the problems. An example of such a system is schematicallyshown in Blauert, The Psychophysics of Human sound, 1983, MIT Presspages 50-51.

It is an object of the invention to provide a sound system as describedin the opening paragraph with improved sound reproduction.

To this end the system is characterized in that the system comprises astoring device for storing sound signals recorded by the microphones,and an input for a recorded signal for reproduction of the recordedsound signal on the headphone through an adaptive filter, the systemcomprising a feed back system comprising the input, the adaptive filter,at least one ear microphone and a comparison means for comparing aninput signal from the storing device to a signal received by themicrophone during reproduction of said input signal, said comparisonmeans providing a comparison signal for regulating the adaptive filter.

In a system in accordance with the invention the detrimental effects ofvariations in transfer function are eliminated or at least reduced. Thedevice comprises comparison means from comparing an input signal to thesignal on the earphone. This enables the signal recorded by themicrophone to be compared during play back to the originally recordedsignal. The recorded signal can on the one hand (as an input signal) besent to the loudspeaker of the headphone through an adaptive filter, onthe other hand the recorded signal (as an output signal) can be comparedto the signal received from the ear microphone giving a comparisonsignal, being the difference between the input and output. The adaptivefilter is regulated with the comparison signal such that the comparisonsignal is minimized. Ideally the comparison signal is made zero, inwhich circumstances the sound signal at the position of the microphoneduring reproduction is exactly the same as the original signal. The feedback loop via the comparison means and the adaptive filter and the factthat the microphone is used for recording as well as during play backeliminates many of the shortcomings of the known systems.

An advantage of the system is also that it is independent of themicrophone transfer function.

Preferably the system comprises a delay for delaying the recorded signalprior to the comparison means.

It takes some time for a signal to pass the adaptive filter, the soundreproduction means (e.g. a headphone) and the ear microphone. Using adelay for the input signal before comparing it to the signal as recordedby the microphone during play back improves the system.

Preferably the system comprises a means to alter the input signal priorto the comparison.

These and other objects of the invention will be apparent from andelucidated with reference to the embodiments described hereinafter.

In the drawings:

FIG. 1 illustrates schematically a system as known

FIG. 2 illustrates schematically a system in accordance with theinvention.

FIG. 3 illustrates schematically a further embodiment of a system inaccordance with the invention.

FIG. 4 illustrates schematically yet a further embodiment of a system inaccordance with the invention.

FIGS. 5A and 5B illustrate schematically yet further embodiments of asystem in accordance with the invention in which head tracking means areincorporated.

FIG. 6 illustrates a carrier for a computer program or computer programcode for use in a system in accordance with the invention.

The figures are schematic and not drawn on scale.

FIG. 1 shows schematically a system as known. The head of a dummy or aperson 1 has a microphone near an ear. An orchestra performs a piece ofmusic.

For simplicity the original piece of music is denoted by signal S1. Arecorded signal S2 is derived form the signal S1 and can be written as(in a somewhat simplified form)S2=S1*transfer function orchestra-head*head related transfer functionduring recording.

There where in this application “transfer function” is written, therelation between one sound signal and another sound signal or one set ofdata and another set of data is meant. This may be a relatively simplefunction, but may also comprise complex matrix multiplication of datausing several matrices.

The orchestra is playing some distance from the head, in a surroundinge.g. an orchestra hall and this modifies the signal S1. This is denotedby “transfer function orchestra-head”. This transfer function isindependent of the shape or form of the head or of the ear shell or earcanal. The second transfer function, the head related transfer functionis dependent, as is clear from the name, from the head, i.e. from e.g.the shape and size of the head, the ear shell, the ear canal.

This signal S2 is the signal at the microphone, This signal is recordedby the microphone to record a signal S3 in a storing device 2 (tape, CDetc). The signal recorded is S3. The microphone itself also influencesthe stored signal S3 which is denoted by the transfer functionmicrophone and thus:S3=S2*transfer function microphone.

This is the stored signal S3. In standard binaural recordings a dummyhead is often used, especially when the microphone is located in the earcanal. Is such recordings the ‘head related transfer function” is thusthe transfer function of the dummy head. When the signal is played backand directly fed to the headphones on a person, the signal S3 is playedback through the headphones to give a signal S4. The signal S3 thusforms an input signal.S4=S3*transfer function headphone

Finally this signal S4 is registered at the ear as a signal S5S5=S4*head related transfer function during play back.

Note that head related transfer functions are often also dependent onthe relative positions of source(s) and head thus the head relatedtransfer function during recording and during play back may not be thesame.

The head related transfer functions are dependent on the head thusdiffer in reality from head to head. In many known systems the data isacquired using a dummy head.

Overseeing the total recording and the playback cycle the relationbetween S1 (the signal from the orchestra) and S5 (the received signalafter recoding and play back) may be written asS5=S1*transfer function orchestra-head*head related transfer functionduring recording(for a dummy head)*microphone transfer function*transferfunction headphone*head related transfer function during play back(forthe person wearing the headphone).

In order to give a true rendition of the actual sound heard, this signalS5 should be the same as the signal S2 as would be received by theperson wearing the headphones, which without some kind of filter wouldnot be the case. Known devices use an equalizing filter 3 to try toaccomplish this. The filter 3 basically multiplies the input signal S3with a filter transfer function Fr.S5=S1*transfer function orchestra-head*head related transfer functionduring recording*microphone transfer function*filter transferfunction(Fr)*transfer function headphone*head related transfer functionduring play back

Ideally the filter transfer function Fr equals (microphone transferfunction*transfer function headphone*head related transfer functionduring play back)⁻¹, i.e. the inverse of the multiplication of themicrophone transfer function, the transfer function of the headphone andthe head related transfer function during play back) giving:S5=S1*transfer function orchestra-head*head related transfer functionduring recording*microphone transfer function*(microphone transferfunction*transfer function headphone*head related transferfunction)⁻¹*transfer function headphone*head related transfer functionduring play back=S1*transfer function orchestra-head*head relatedtransfer function during recording=S2.

When a dummy head is used for recordings the transfer function of thefilter would ideally also take into account the difference between thehead transfer function of the dummy head during recording and thetransfer function of the real head during play back. The transferfunctions to be used by the filter 3 can, however, only be estimated ortheoretically derived. The transfer function needs to be calculated andthe calculation introduces errors. For each frequency the transferfunction has to be determined, which either requires a large calculationeffort and such calculation in itself may be a source of error ornecessitates the use of average transfer functions for a band offrequencies, which also introduces errors. All transfer functions arealso to some extent dependent not just on the relative positions of thesound sources (real or phantom) and the ears, but also on other factors,such as objects near the sources or ears which may reflect or alter thesound waves and thus influence the transfer functions.

Especially for the higher frequencies, the transfer functions aredifficult to determine because of the shape of the head and the earcanal and differ from person to person and even may be dependent onfactors such as wearing a hat. In short the Head Related Transferfunction, HRTF, is a highly individual one. Even relatively simpletransfer functions such as the microphone transfer function and thetransfer function for the headphone have to be calculated and aresometimes more complex than one would think.

The filter 3 has in the known systems a fixed filtering function whichcan only be some average filtering function incapable, even if therewould be no problems with calculating the transfer function (which thereare), of taking into account influences which are from the outsetunknown, such as the shape and size of the head, the ear canal,temperature, whether or not the user is wearing a hat etc.

In short in the known systems any transfer function needs to becalculated and the calculation introduces errors, for each frequency thetransfer functions have to be determined, which either requires a largecalculation effort and such calculation in itself may be a source oferror or necessitates the use of average transfer functions for a bandof frequencies, which also introduces errors and all transfer functionsare to some extent dependent also on other factors, such as objects nearthe sources or ears which may reflect or alter the sound waves and thusinfluence the transfer functions and temperature. No fixed transferfunction can take into account such dependence nor can it take intoaccount difference between transfer functions for different heads.

Thus, using the known system a true-to-life like reproduction isdifficult to attain and there is a need to improve the soundreproduction. A person will never hear what he has heard during aconcert (or soccer match or anywhere where he/she was). Truly relivingthe experience is therefore difficult, if not impossible. It is remarkedthat many systems offer the possibility to “improve” the sound quality,or even automatically improve the sound quality. To bring back thememories a true-to-life play back or at least a close to true-to-lifeplay back is needed. It is an object of the invention to provide for asystem which provides the possibility for an improved true-to-life playreproduction of the sound. The aim of the invention is to provide asystem which does enable a more true-to-life rendition.

FIG. 2 illustrates a preferred embodiment of a system in accordance withthe invention, shown in this figure for the right ear only.

The system comprises one or more microphones M_R in or near the ear.This microphone registers the sound and via the microphone a record ismade on a storing device 2 (in this figure also denoted by ST). Duringrecording the switch S_(a) is set such that the signals are sent to therecording device 2 (indicated by the drawn line in switch S_(a)). Duringplayback the switches are changed, indicated by the dotted lines in theswitches and the signal S3 from the storing device 2 is fed to a soundgenerating system, in this example a headphone LS_R via an adaptivefilter 21. The signal S3 thus forms an input signal for a feed-backsystem 25 indicated by the elements within the dotted lines. Via inputmeans 24 this input signal is fed to the feed-back system. Themicrophone is more or less at the same position as during recording andregisters the sound S5 received as the music is played back. In acomparator 22 the signal S6 received and transmitted via the microphone(S6 equals S5*transfer function microphone) is compared to the storedsignal S3, and the result of this comparison, an error signal “e” isused to regulate the adaptive filter function AFr of an adaptive filter21. The feed back system 25 enables the input signal S3 (at the input24) and the received signal S6 to be made substantially the same, thedifference of the signals S6 and S3 (S6-S3) substantially equaling zero.

This leads to the following set of equations:S3=S1*transfer function orchestra-head*head related transfer functionduring recording*microphone transfer(as in the prior art)S5=S1*transfer function orchestra-head*head related transfer functionduring recording*microphone transfer function*adaptive filter 21transfer function AFr*transfer function headphone*head related transferfunction during play backand (as a result of the use of the microphone during play back and ofthe comparator 22)S6=S5*microphone transfer function(signal via microphone during playback) S6=S3(both sides of the comparator 22)This givesS6=S3*microphone transfer function*adaptive filter 21 transferfunction*transfer function headphone*head related transfer functionduring play back andS6=S3giving:microphone transfer function*filter transfer function*transfer functionheadphone*head related transfer function during play back=1giving:AFr=filter transfer function of adaptive filter 21=(microphone transferfunction*transfer function headphone*head related transfer functionduring play back)⁻¹

This may seem the same result as in the known device of FIG. 1, but forimportant differences, e.g. the microphone transfer function in signalS3 is per definition the same as the microphone transfer function insignal S6, without the need to calculate or estimate the microphonetransfer function. This reduces errors. The head transfer functions arereal personalized head transfer functions, not those from dummy heads,again taking away or at least reducing another source of errors. Noestimations or calculations with their inherent errors are needed.Overall a much more life-like rendition of sound, i.e. the same asoriginally will be attained. In short the system comprises a storingdevice 2 for storing the sound signals S3 as recorded by the microphone,and a means for reproducing the recorded sound signal on the headphonethrough an adaptive filter 21, and a means 22 for comparing the storedsignal S3 to a signal received by the microphone upon duringreproduction S6, said comparison means providing in operation acomparison signal e for adaptively regulating the signal send to theheadphone.

It is to be noted that the function of the feedback system is such as toset the settings of the adaptive filter 21 such that the signals at bothsides of the comparator 22 are equal (S3=S6, i.e. e=0). This isindependent of the nature of the input signal S3 on input 24 of the feedback system. In a preferred embodiment of the device in accordance withthe invention use of this circumstance is made. When the listeneractivates the sound reproduction means a gauge signal (e.g. white noise)is briefly used as the input signal on input 24 (this signal does notnecessarily have to have been recorded beforehand by the microphone(s)).Prima facie this seems superfluous and only bothersome, however, itenables to find gauge values for the filter characteristics AFr in afast and efficient manner. The advantage is that when thereafterrecorded music is played, the settings of the filter AFr are good ornearly good, so that no or only little changes to these settings have tobe made. It has to be remembered that some music parts may have only lowfrequency sounds or certain frequencies do not appear than after sometime, so at least during the initial stages of listening to the recordedmusic the adaptive filter is still adapting. Using a gauge signal it ispossible to find the settings for the complete frequency range veryrapidly. In preferred embodiments the settings for a person, once found,may be stored, so that the next times the same person uses the system,the starting values of that person are used to find the correct values,reducing time needed for the gauging procedure.

Preferably the system comprising a delay element or delayer 23 to delaysignal S3 a time Δt before it is compared to signal S6. In the system ittakes some time for signal S3 to travel through the adaptive filter, viathe headphone (S4) and the microphone (S5) back to the comparator (S6).Using a delayer this time delay can be taken into account. It isremarked that the comparator and the adaptive filter may be somephysical circuit, in which case the delay is formed by e.g. asub-circuit. However, all or some of these functions may be done insoft-ware, i.e. using a computer program, for instance a delay of timeΔt can be implemented by comparing the data of the signal S6 with storeddata, i.e. using a pointer.

The equation would then be, t_(playback) being real time, i.e. the timeat which the signal S6 is recorded:S6(t _(playback))=S3(t _(playback) −Δt) (if error e=0)

Or in other words the recorded signals S6 are compared, using somecomputer program or program code, with stored data S3 of some time inthe past and the filter functions are such adapted that the error e issubstantially zero.

Likewise the filter function can be some filter circuit with inputs, butcan and often will be formed in software, i.e. a computer program orcomputer program code performing the function of a filter having inputdata S3, input data for regulating (i.e. setting the adaptive filter)coming from the comparison, and output data to be sent to the headphone.Especially when using digital recording and sound reproduction use ofcomputer programs or computer program code will be made. Within theconcept of the invention some of these functions may be embodied in hardware while others may be embodied in software. Within the concept of theinvention the words “filter” “means for filtering” and “comparator”“means for comparing”, “delay” etc. are to be broadly understood and tocomprise e.g. any piece of hard-ware (such filter circuit or filter,comparator, delay line), any circuit or sub-circuit designed forperforming a filtering action, delay action, comparison as described aswell as any piece of soft-ware (computer program or sub program or setof computer programs, or program code(s)) designed or programmed toperform a filtering, delaying, comparing operation in accordance withthe invention as well as any combination of pieces of hardware andsoftware acting as such, alone or in combination, without beingrestricted to the given exemplary embodiments.

The invention is also embodied in any computer program comprisingprogram code means for use in a system in accordance with the inventionwhen said program is run on a computer as well as in any computerprogram product comprising program code means stored on a computerreadable medium for use in a system in accordance with the inventionwhen said program is run on a computer and as well as any computerreadable medium (CD-Rom, cassette or other carrier) comprising suchcomputer program code means or computer program product.

FIG. 3 illustrates an embodiment of the invention.

The system has been provided with a setting device 31. Using thissetting device the user may alter the signal data S3 before thecomparator 22 and filter 21. Prima facie this may seem to offer acontradiction. The object of the system is to provide a true-to-lifereproduction, using an adaptive filter 21. It would seem that changingthe signal using the setting device would lead away from this object.

However the object of the invention is to provide a system offering thepossibility for a true-to-life reproduction, not necessarily forcing theuser to only a true-to-life reproduction. Offering the possibility tochange the data using the setting device 31 is not contradictory to thisobject, but only offers extra possibilities. The user might want tochange the settings. He/she would then possibly hear something else thanhe/she had heard originally, for instance louder, but if the user wantsto hear what was recorded louder, the preferred embodiment allows this.

The first function which could be set is the volume of the soundenabling the user to hear more the music more loudly.

A further function which may be set is the distribution between tones(for instance emphasizing the higher frequencies more).

In fact, the setting device enables in circumstances, a moretrue-to-life experience by the listener than without the use of asetting device.

As people age, the sensitivity of the ear itself changes, basically itbecomes less sensitive and the sensitivity for higher frequencies becomeless. Similar effects occur due to a common cold or due to fatigue. Thesame sound at the ear is then perceived differently. Ideally, however,the listener will perceive the same sound. To some extent these effectscan be counteracted by turning up the volume and changing thedistribution over the frequencies, thus offering the possibility to comecloser to the experience the listener once had even though the hearinghas become less. Of course the decline in hearing can only be partiallycounteracted, but nevertheless the setting device 31 can be useful inenabling to come closer to the goal of reliving the experience.

All examples given so far show one ear only. FIG. 4 show an arrangementfor two ears. The system is of course a double rendition of the systemshown in FIGS. 2 and 3, but there is in addition a further preferredcharacteristic. To take into account cross talk between the left andright ear, the left ear signal is send to the right ear adaptive filterand vice versa.

It will be clear that within the framework of the invention manyvariations are possible. It will be appreciated by persons skilled inthe art that the present invention is not limited by what has beenparticularly shown and described hereinabove. The invention resides ineach and every novel characteristic feature and each and everycombination of characteristic features. Reference numerals in the claimsdo not limit their protective scope. Use of the verb “to comprise” andits conjugations does not exclude the presence of elements other thanthose stated in the claims. Use of the article “a” or “an” preceding anelement does not exclude the presence of a plurality of such elements.

Further variations may for instance be formed by: In addition to soundrecorded by the microphones near or in the ear, also other things can berecorded on the storing device 2, e.g. power point files orrepresentations, video's or web camera's parameters describing theset-up during the recording, the head movements (which may e.g. bemeasured by a head-tracker) during a recording can be recorded. In thelatter case a compensation during the reproduction can be derived.

The recorded data can be encoded. Other parameters, like the boneconduction of a speaker can be recorded, enabling to reproduce the soundof a speaker how he actually perceives his own voice, “Storing device”should be interpreted broadly, e.g. the data can be transmitted or evenbroadcasted or the storing device could be a recording device enablingthe data to be stored on a disk for later replay. The data is stored orrecorded somewhere on some data carrier for play back. The data itselfhowever, need not be stored in the system itself, but on some datacarrier which is removable from the system itself. So a storing deviceis a unit for storing the data whether it is stored inside the systemitself (on a hard disk for instance) or on a removable carrier (a CD-Romfor instance) or broadcasted or transmitted to some device outside thesystem itself for storing by such a device. So, within the concept ofthe invention the term storing device(s) comprise devices for sendingdata as they are recorded via some sort of transmission (IRtransmission, cable, internet etc) to a data storage device. The storagedevice (i.e. were the recorded data are kept) itself may be part of butmay also be remote form the system in accordance with the invention. Insuch cases the system in accordance with the invention would comprise acommunication device for sending recorded data to a remote storagedevice (in itself not part necessarily part of the system), saidcommunication device forming the storing device, since its function isto send recorded data to a storage device for storing, thus to store (toput into storage) the recorded data.

If during recording head movements are made which will not be madeduring play back, then the influences of these movements on the signalcan be made undone, or the other way around, if there are head movementsduring play back mode, which were not made during the recording stage,the signals can be altered in such a way that it corresponds with themovements. Thus in preferred embodiments the system comprises means forrecording head movements. FIG. 5A illustrates such an embodiment. Thesystem comprises a system for recording head movements. In this examplethe system comprises a number of fixed points 53, 54 and a number ofdevices 51, 52 on the head. Sending a signal (e.g. an IR signal) fromthe head to the fixed point or vice versa, it is possible to establishthe orientation of the head in respect of the fixed points. Assumingthat in this example the receivers are located on the head, the signalsof the receivers 51, 52 are fed into the storing device 2, thusrecording the position and orientation of the head vis-à-vis the fixedpoints are thereby the head movements. The head position signals arestored. Upon replay the head position may be compared to the headposition during play-back and this may be used as an input to a alteringdevice 31 to alter the data so that account can be taken of the headmovements, during recording, during play back and/or of differences inhead position. This is schematically indicated in FIG. 5B where acomparison is made in comparator 55 between signal coming from the headtracking devices during playback with stored data from storing device 2.This difference is an input in device 31 which in this example comprisesa delay and filter to correct for the position of the head during playback in relation to that during recording. Making use of sources andreceivers enables a good tracking of the head movements. However,especially during recording such an elaborate system may not always beavailable. In such case use may nevertheless be made of head trackingdevices to track head movements without using a system of sources andreceivers. The position of the head in respect of the vertical axis mayfor instance be relatively accurately and easily be measured using tiltsensors, which generate a signal corresponding to an angle to thevertical axis. Movement sensors may be used to track movements in otherdirections. The head tracking device(s) may comprise or be comprised ofvideo camera's. By analyzing video data head movements may be(re)constructed. It is remarked that in embodiments of the system inaccordance with the invention the system may comprise video cameras (ora video camera) for simultaneous recording of video data, even if thevideo cameras do not function as a head tracking device. The necessarystorage for the adaptive filter can be implemented by the storage device‘ST’ as well. Since, all necessary data occurring in the FIR filter forthe adaptive filter is available in ‘ST’ already. With the use ofpointers this can easily be realized.

In simple set-ups the system will have one ear microphone per ear,however this is not a restriction. In more complex, preferredembodiments more than one, i.e. a system of microphones made by used foreach ear. The microphone registers the sound at the position of themicrophone. What is actually heard is, however, the sound at theposition of the ear drum. The system in accordance with the inventionenables a true to life reproduction of sound at the position of themicrophone. Small discrepancies may nevertheless occur in regards of thesound at the eardrum. Using more than one microphone, thus making surethat at several positions close to the eardrum a true-to-life soundreproduction is achieved, reduces such discrepancies and therebyimproves the system.

In the shown examples the sound reproduction means comprises headphones.This forms a preferred embodiment. However, the sound reproduction meansmay be other sound reproduction means for instance two loudspeakers in acar, also the number of sound reproduction means per ear or per systemmay vary.

Into the system further recording devices (e.g. for recording video) maybe incorporated.

FIG. 6 illustrates schematically a computer readable medium (CD-Rom,cassette or other carrier) comprising a computer program code means orcomputer program product in accordance with the invention.

The invention is also embodied in a method for recording andreproduction of sound through ear microphones and sound reproductionmeans in which method

sound data are recorded by ear microphones

said sound data is stored on a storage device

said recorded sound data is reproduced during which reproduction therecorded

data is reproduced on sound reproduction means

said recorded sound data forming input data for a feed back system (25)comprising an input (24), an adaptive filter (21), at least an earmicrophone (M_R, M_L), at least one sound reproduction means (LS_R,LS_L) and a comparison means (22) for comparing an input signal (S3) toa signal received by the microphone (S6) upon during reproduction ofsaid input signal (S3), said comparison means (22) providing acomparison 25 signal (e) for regulating the adaptive filter (21).

The invention is further also embodied in A sound reproduction systemcomprising ear microphones and sound reproduction means for generatingsound and means to control the sound signal generated by said soundreproduction means, characterized in the system comprises an input (24)for a recorded sound signal (S3) for a sound signal on the means forgenerating sound (LS_R, LS_L) through an adaptive filter (21), thesystem comprising a feed back system (25) comprising the input (24), theadaptive filter (21), at least an ear microphone (M_R, M_L), at leastone sound reproduction means (LS_R, LS_L) and a comparison means (22)for comparing an input signal (S3) to a signal received by themicrophone (S6) during reproduction of said input signal (S3), saidcomparison means (22) providing a comparison signal (e) for regulatingthe adaptive filter (21).

As stated above, the signal at the input (24) may be any signal, and thefeed back system ensures that there is an equivalence between the inputsignal S3 and the signal S6. This is advantageous since a number oftransfer functions which otherwise would have to be calculated withinherent inaccuracies are in the sound reproducing system automaticallycorrect.

1. A sound recording and reproduction system comprising: ear microphonesfor recording sound; sound reproduction means for generating sound; andmeans to control the sound signal generated by said sound reproductionmeans, characterized in that the system comprises: a storing device (2)for storing sound signals recorded by the microphones (M_R, M_L); aninput (24) for reproduction of a recorded sound signal (S3) on the meansfor generating sound (LS_R, LS_L) through an adaptive filter (21), thesystem comprising a feed back system (25) comprising the input (24), theadaptive filter (21), at least one ear microphone (M_R, M_L), at leastone sound reproduction means (LS_R, LS_L) and a comparison means (22)for comparing an input signal (S3) to a signal received (S6) by themicrophone during reproduction of said input signal (S3), saidcomparison means (22) providing a comparison signal (e) for regulatingthe adaptive filter (21).
 2. A sound recording and reproduction systemas claimed in claim 1, characterized in that the sound reproductionmeans are headphones (LS_R, LS_L).
 3. A sound recording and reproductionsystem as claimed in claim 1, characterized in that the system comprisesa delay element (23) for delaying the recorded signal prior to thecomparison means (22).
 4. A sound recording and reproduction system asclaimed in claim 1, characterized in that the system comprises a means(31) to alter a recorded signal prior to the input of the feed backsystem (25).
 5. A sound recording and reproduction system as claimed inclaim, characterized in that the system comprises head tracking means(51, 52, 53, 54).
 6. Computer program comprising program code means foruse in a system in accordance with the invention when said program isrun on a computer.
 7. Computer program product comprising program codemeans stored on a computer readable medium for use in a system inaccordance with the invention when said program is run on a computer. 8.Computer readable medium (CD, cassette or other carrier) comprising acomputer program code means or computer program product as claimed inclaim
 7. 9. Method for recording and reproduction of sound through earmicrophones and sound reproduction means in which method sound data arerecorded by ear microphones said sound data is stored on a storagedevice said recorded sound data is reproduced during which reproductionthe recorded data is reproduced by sound reproduction means saidrecorded sound data forming input data for a feed back system (25)comprising an input (24), an adaptive filter (21), at least an earmicrophone (M_R, M_L), at least one sound reproduction means (LS_R,LS_L) and the input data (S3) are compared in a comparison means (22) toa signal received by the microphone (S6) during reproduction of saidinput data (S3) and by said comparison means (22) a comparison signal(e) for regulating the adaptive filter (21) is provided.
 10. Computerprogram product comprising program code means stored on a computerreadable medium for use in a method in accordance with the inventionwhen said program is run on a computer.
 11. Computer readable medium(CD, cassette or other carrier) comprising a computer program code meansor computer program product as claimed in claim
 10. 12. A soundreproduction system comprising ear microphones and sound reproductionmeans for generating sound and means to control the sound signalgenerated by said sound reproduction means, characterized in that thesystem comprises an input (24) for a recorded sound signal (S3) on themeans for generating sound (LS_R, LS_L) through an adaptive filter (21),the system comprising a feed back system (25) comprising the input (24),the adaptive filter (21), at least one ear microphone (M_R, M_L), atleast one sound reproduction means (LS_R, LS_L) and a comparison means(22) for comparing an input signal (S3) to a signal received by themicrophone (S6) during reproduction of said input signal (S3), saidcomparison means (22) providing a comparison signal (e) for regulatingthe adaptive filter (21).